Olefin with high stereoselectivity

Recently, Kantam et al. have performed the cross-coupling reaction of MBH adducts with arylboronic acids by using rhodium-exchanged fluorapatite catalyst (RhFAP), which was prepared by treatment of fluorapatite (prepared by incorporating basic species F in apatite in situ by coprecipitation) with an aqueous solution of RhCls. Various arylboronic acids and MBH adducts were converted into the corresponding trisubstituted olefins with high stereoselectivity, demonstrating the versatility of the reaction. The catalyst (RhFAP) was recovered quantitatively by simple filtration and reused with almost consistent activity (Scheme 3.102). ... 

PET reactions [2] can be considered as versatile methods for generating radical cations from electron-rich olefins and aromatic compounds [3], which then can undergo an intramolecular cationic cyclization. Niwa and coworkers [4] reported on a photochemical reaction of l,l-diphenyl-l, -alkadienes in the presence of phenanthrene (Phen) and 1,4-dicyanobenzene (DCNB) as sensitizer and electron acceptor to construct 5/6/6- and 6/6/6-fused ring systems with high stereoselectivity. 

In acceptor-substituted carbene complexes with hydrogen at Cp fast hydride migration to the carbene will usually occur [1094,1095]. The resulting olefins are often formed with high stereoselectivity. 1,2-Hydride migration will also occur in P-hydroxy carbene complexes, ketones being formed in high yields (Table 4.2). Intramolecular 1,5-C-H insertion can sometimes compete efficiently with 1,2-insertion [1096]. 

Other terminal olefins were transformed to the corresponding cyclopropane esters with Z-menthyl and d-menthyl diazoacetates with high stereoselectivity up to 98% ee (Scheme 3). Intramolecular reaction of the phenyl-allyl ester 9 was carried out to give the bicyclic compound 10 with 86% ee and 93% yield. The enantioselectivity for intramolecular cyclopropanation of the 3-methylbutenyl ester 11 was compared with chiral Cu(I), Rh(II), and Ru Pybox catalysts Rh>Ru>Cu [26]. 

Like a,/Lunsaturated carbonyl compounds, vinyl silanes and particularly vinylsiloxanes do not dimerise readily and can thus be used in excess to drive selective CM reactions. Pietraszuk et al. [56] have exploited this to couple vinyl-triethoxysilane with a variety of olefin partners in good yield and with high stereoselectivity (Scheme 8) [57]. Given the importance of vinylsiloxanes as nucleophilic components in Pd-catalysed coupling reactions [58], their facile and stereoselective modification by CM is a significant development. 

The addition of trimethylsilylphenylsilylene to the olefin proceeds with high stereoselectivity to give the silacyclopropane. Thus, irradiation of... 

Cross-coupling between 1-alkenyl- and arylboron compounds with organic electrophiles have found wide application (see Sect. 1.5.1.1) in organic synthesis [125, 132, 269-271]. The value of this methodology is further realized with the use of alkylboranes, such as B-alkyl-9-borabicyclo[3.3.1]nonanes (B-R-9-BBN), which can be conveniently prepared Ijy hydroboration of olefins [272]. The hydroboration proceeds with high stereoselectivity and chemoselectivity. The choice of phosphines in a catalytic system sometimes affects the chemo- and regioselectivity of the hydroboration. Hydroboration of l-(ethylthio)-l-propyne with catecholborane can be satisfactorily carried out with PdClj (dppf) but the regioselectivity is best for the dppe and dppp complexes of Ni [273]. Notably, PPhj complexes perform poorly. 

An Interesting method for formation of a-vinylene lactones relies on sulfur for activation of the a-position. Condensation of the anion of the thiocarbonate with a variety of aldehydes gives olefins in moderate to excellent yields with high stereoselectivity. ... 

Due to their singlet character, carbenes with sulfur-, selenium-, silicon-, or tin-substituents add to olefins with high stereospecificity, thus guaranteeing mechanism-based stereoselectivity. While high simple diastereoselectivity has been observed in certain examples, the diastereofacial selectivity of these carbenes is almost unknown, and examples of enantioselective carbene transfer reactions are completely lacking. 

Asymmetric halolactonization is a much used procedure for the stereoselective formation of C — Br and C —I bonds (see also Sections D.4.6. and D.7.2.). This intramolecular reaction is used to transfer chiral information in the molecule over three or four bonds, sometimes with high stereoselectivity. Formation of a halonium complex with the olefin is the first step of the reaction followed by intramolecular lactonization. Induction of asymmetry is achieved in different ways. 

The reaction of nitrone 101 with such olefins 5 as propylene, n-hexene, allyl alcohol, styrene, acrylic acid, methyl acrylate, acrylonitrile, and butadiene are all regiospecific to give S-substituted isoxazolidines of type l.77 The reaction with olefins 6 seems to be regio- and stereo-specific thus, nitrone 101 and methyl methacrylate give cycloadduct lilt as the sole product.77 Similarly, 101 and 1 -methyl-1-phenylethylene gives adduct Hit.77 In the reactions with olefins 7 or 8, the stereospecificity is more evident.77,78 The isoxazolidine obtained is always one of the two possible epimers. The reaction of nitrone 101 with trisubstituted olefins is highly stereoselective.64 Some results are summarized in Table III. 

An alternative route by the Danishefsky group was developed [142e-g] (Scheme 84). The aldol reaction of ethyl ketone 580, prepared from P-keto ester 579, with aldehyde 581 stereoselectively afforded 582 (dr = 5.4 1). After Troc protection followed by hydrolysis of the enol ether, Suzuki coupling with 583 followed by TBS deprotection gave the desired (12Z)-olefin 584. The Noyori reduction of the P-keto ester 584 gave 3a-alcohol with high stereoselectivity, which was converted into hydroxy carboxylic acid 585. Macrolactonization of 585 was accomplished by the Yamaguchi method, and subsequent deprotection and DMDO oxidation efficiently afforded epothilone B (5b). 

Intramolecular acyliminium-ion cyclization of 870 produces 871 with high stereoselectivity. Ozonolysis of the olefin affords 872 (the totally chiral version of 863). Lithium aluminum hydride reduction of 872 gives (— )-dihydroxyheliotridane (851) in 93% yield. 

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